This invention relates to an apparatus for dispensing single doses of gaseous radioisotopes to a patient.
Radioactive isotopes of xenon and other radioisotopes are useful in the field of medicine and particularly in medical diagnosis. There is increasing use of xenon-133 in the medical field for studying blood flow in muscles, scanning the lungs for lung functional disorders (e.g., emphysema and emboli), scanning the brain and scanning for cardiac abnormalities. For scanning of the lungs, xenon-133 can be introduced into a human body by one of two processes. In an inhalation process, the patient breathes a gas containing xenon-133 and the xenon-133 is drawn directly into the patient's lungs. In an injection process, a saline solution containing dissolved xenon-133 is injected into the blood stream of the patient and through perfusion the xenon-133 goes to various organs of the patient, including the patient's lungs. Radioactive gases having more optimum imaging characteristics for specific purposes may also be used, such as xenon-127.
One current practice of formulating a xenon-133 solution for medical applications is to dissolve the xenon-133 directly into a saline solution to achieve gas concentrations appreciably below saturation of the xenon-133 in the solution at the temperature of dissolution. This avoids any occurrence of bubble formation in the solution during use. In further detail, the present procedure used in the medical profession for preparing injectable doses of xenon-133 as an aqueous solution involves crushing an ampoule containing xenon-133 in a container filled with a normal saline solution.
The difficulties in handling and storage of xenon and in particular of a radiopharmaceutical xenon-133 solution are set forth in the Journal of Nuclear Medicine in Volume 11 at page 352 (1970) and Volume 13 at page 231 (1972). These difficulties can be summarized as follows: (a) there is loss of xenon-133 into air spaces resulting as individual doses are removed from multidose vials since it is difficult to prevent the introduction of air bubbles when replacing the volume withdrawn from the vial; (b) there is diffusion of xenon-133 into rubber components in contact with the xenon-133 such as in elastomeric systems at the end of cylindrical glass capsules and rubber septums on multidose vials; and (c) there is diffusion of xenon-133 into both the plastic and rubber components of disposable syringes used for injection of the patient.
Studies have been made regarding the trapping of radioactive xenon in various materials, and these studies show that elastomers and a variety of materials will take up significant quantities of radioactive xenon. As a result of these studies, only glass syringes, which take up less than 1% of the xenon-133 from the solution, are used for dispensing such radioactive xenon solutions. However it has remained desirable to minimize the foregoing difficulties and to further reduce the loss of radioactive xenon isotopes to the materials used to package doses of the radioactive xenon isotopes.
The widest use of xenon-133 is in pulmonary function studies and this involves having the patient inhale a dose of gaseous xenon-133, and while the patient holds his breath a scintillation camera is used to take a picture of the patient' s lungs. This picture shows any portions of the patient's lungs not functioning or not properly functioning.
The use of xenon-133 in pulmonary function studies has required quantities of xenon in patient dosage sizes accurately measured and readily administered to the patient. There have been several devices designed for holding and administering dosage sized quantities of gaseous radioactive xenon to patients, and design of such devices has attempted to meet the following requirements, namely ease and safety in administration to the patient; effective radiation shielding during shipment, storage and handling incidental to administration to the patient; a container insuring substantial retention of the radioactive xenon prior to administration to the patient; a container suitable for re-collection of the radioactive xenon after administration to the patient; a system capable of providing multiple administrations to the patient; absence of absorption of the radioactive xenon by the materials holding the dosage size quantity of radioactive xenon; and a dispensing device providing a high concentration of xenon in one inhalation.
One device for holding and administering dosage sized quantities of gaseous radioactive xenon is a Calidose gas dispenser shown in FIG. 1. This dispenser unit 10 is loaded with a glass vial 11 closed off with an elastomeric septum 12 and the glass vial 11 holds the gaseous xenon prior to administration to a patient. The dispenser unit 10 has a manually operated plunger 13 for pushing the septum 12 in the glass vial 11 against two hollow needles 14 and 15 for puncturing the septum 12. A manually operated rubber squeeze bulb 16 is connected to one hollow needle 15 and flushes the xenon from the glass vial 11 through the other hollow needle 14 into a nozzle 17 and into a breathing apparatus (not shown) held in the patient's mouth.
Another device for discharging quantities of gaseous radioactive xenon is shown and described in Volume 92 of Radiology at pages 396-7 (February, 1969). A gas cylinder containing radioactive xenon is filled with carbon dioxide to a pressure of 3 atmospheres giving a xenon-carbon dioxide mixture in the cylinder. A small quantity of the mixture is withdrawn from the cylinder through a micrometer needle valve. The amount of xenon-133 dispensed can be measured by placing the syringe inside a calibrated well-type ionization chamber. Radioactive xenon gas which is to be used in a closed-circuit spirometer system can be taken up into a Hamilton gas-tight syringe for transfer.
Another procedure is to use a hypodermic syringe to inject air into an ampoule sealed by a septum containing radioactive xenon and then to withdraw a fraction of the air-xenon mixture. The syringe is exhausted into a closed-circuit spirometer and the patient breathes the gases in the closed-circuit spirometer. This also has the septum absorbing a portion of the radioactive xenon.
Accordingly it has remained desirable to have a xenon dosage dispensing apparatus for patients providing a patient sized dose of radioactive xenon.